People use display screens for a wide variety of purposes. For example, display screens may be used to display specific information from devices such as oscilloscopes, radars, televisions, projection systems, and other types of electronic instruments. The information may be shown on many types of display screens such as cathode ray tubes ("CRT"), liquid crystal displays ("LCD"), and gas plasma displays.
Display screens are also frequently used in conjunction with computers. Computers are used for many purposes, including personal, educational, and work uses. People often view these display screens for extended periods of time. Extended viewing of the screen can cause eye strain and eye fatigue, leading to physical and mental discomfort for the viewer. This problem is becoming increasingly prevalent as more jobs and businesses require employees view display screens for extended periods of time.
Cathode ray tubes are a very common type of display screen used with computers. Cathode ray tubes are also used in a wide range of other applications including television picture tubes, video monitors, and oscilloscopes. As is well known, a cathode ray tube includes an electron gun which emits a stream of electrons. A first anode focuses the electrons into a narrow beam and accelerates the electrons to a greater speed. A second anode gives the electrons still more speed. Deflection coils or plates surrounding a portion of a cathode ray tube control the location at which the electron beams strike the inner surface of the display screen. The inner surface of the display screen is typically coated with a phosphor material which glows when struck by an electron to create an individual point of light.
A typical cathode ray tube display screen includes thousands of these individual points of light which create the desired image on the display screen. As is well known, a pixel or picture element is a small logical unit that is used to build an image on the display screen. A single pixel is usually created by several adjoining points of light. The fewer the dots of light used to create a pixel, the higher the resolution of the display screen.
It is known to utilize cathode ray tubes to create a color display. The color monitors that were originally used with devices such as computers had relatively crude color and graphics, and many could display only four basic colors. Current monitors, however, commonly have a palette of 256 colors. In fact, many color monitors now have the capacity to display thousands of colors. Modern monitors also often include a larger number of pixels than the older monitors, and this allows the desired image to be more accurately represented on the screen.
A typical cathode ray tube color monitor contains three electron guns, one gun for each color of red, green and blue. The electron guns send out a stream of electrons which strike the phosphors of a particular color coating the inside surface of the screen. In general, the amount of light that a particular phosphor emits is dependent upon the strength of the electron beam which strikes a given phosphor because the stronger the electron beam, the more light the phosphor emits. For example, if every red, green and blue dot in a particular pixel is struck by equally intense electron beams, the result is a white dot. As is well known, different colors, shades and brightness are obtained by varying the intensity of the electron beams striking that pixel.
After the electron beam leaves a particular phosphor, the phosphor continues to glow briefly, a condition called persistence. For an image to remain stable, the phosphor must be reactivated by repeated scans of the electron beam. When the fading of the phosphor between repeated scans of the screen becomes noticeable, the screen flickers. This flicker is ordinarily considered undesirable. Accordingly, the monitor must continually re-energize the various phosphors in the display to eliminate flicker. This continual redrawing or re-energizing of the display is the monitor's refresh rate. With a high refresh rate, the screen is more frequently redrawn and the eye of the viewer tends to see a smooth, nonflickering display. A typical cathode ray tube has a refresh rate of between about 60 and 70 cycles per second.
Early cathode ray tube display screens could only turn a particular pixel in the display on or off. This made it difficult to achieve subtle distinctions in colors because an energized pixel displayed only a single color at the same brightness. In contrast, current display screens often utilize a variable-graphics-array ("VGA") display adaptor which allows the strength of the different electron beams to vary so that the color and brightness of each pixel can be varied. This allows the monitor to display a wide range of colors because the brightness and color of each pixel is individually controlled.
In further detail, a typical cathode ray tube display used with a computer system receives signals from sources such as the operating environment or application software, and these signals are sent to the input/output hardware of the computer, which frequently contains the VGA display adaptor (the VGA display adaptor is often built into the motherboard of a personal computer). The VGA display adaptor processes the signals through a circuit called a digital-to-analog converter ("DAC"). Frequently, the digital-to-analog converter is contained within a specialized chip. Often this specialized chip contains three digital-to-analog converters in order to control the three colors used in the display.
As is known in the art, the digital-to-analog converter compares the values sent by the computer to a table that contains the matching voltage levels for the three colors needed to create the particular color and brightness. A precise amount of voltage from each electron gun then energizes each pixel to reproduce the desired color and brightness.
As the number of colors increases and the resolution of the display screens improve, a more realistic display is created, which allows more information to be conveyed to the viewer. This improved display has increased the number of users of display screens, and the amount of time which people view display screens.
Typically electronic display screens allow the brightness or intensity of the screen to be adjusted for different lighting conditions. A known method to adjust the brightness of a display screen is to use a variable resistor or potentiometer. The potentiometer allows the intensity of the electron beams to be controlled, and this allows the brightness of the display screen to be adjusted. Conventionally, a protruding knob or other rotatable member, often labeled as a brightness control knob, is connected to the potentiometer such that the user can manually adjust the brightness of the screen.
It is also well known to use a liquid crystal display ("LCD") screen for a wide variety of purposes. For example, LCDs are frequently used with computers, especially portable or notebook-type computers. As is known to one of ordinary skill in the art, LCDs are electronically switched display panels that make use of changes in the reflective properties of liquid crystals in series with an electronic field. LCDs often include a backlight or other lighting source such that a person can read the display in various lighting conditions.
Some display screens connected to a computer allow the brightness of the screen to be adjusted by the computer. For example, the Macintosh Powerbook sold by Apple Computer, Inc. allows the user to adjust the backlight of the LCD screen. The backlight of the screen is typically controlled by entering one or more commands through the keyboard or mouse of the computer. Alternatively, the backlight may be controlled by the computer executing an application or third-party software program. For example, the backlight brightness for the Powerbook computer may be adjusted by software which controls the backlight driver. As well known to one of ordinary skill in the art, the backlight driver is a standard MacIntosh driver that can be controlled by a series of commands or calls, and these calls may be used to set or change the backlight of the screen to the desired level.
In addition, some display screens may allow the color to be adjusted by a computer. For example, a company called MAG Innovision of Santa Ana, Calif., sells a product called Advanced Display Calibration which allows commands entered through a keyboard or mouse to control the color of a computer monitor.
Accordingly, the brightness and/or color of a display may be controlled by a system having these or similar capabilities.